This invention relates to an earthing or grounding structure enabling both a ground terminal and a ground lug to be in continuity even with the same shell structure for grounding, and more particularly to an electrical connector using the grounding structure for use in machine tools, robots and the like.
A commonly used electrical connector at least includes a plurality of contacts, a housing for holding the contacts, and a shell for holding the housing. Moreover, said electrical connector has an earthing or grounding structure for causing a ground terminal or ground lug to be in continuity with said shell for connecting a protection circuit as a safety measure. An earthing (i.e., grounding) structure has been disclosed in the following Patent Literature 1 or the like.
Patent Literature 1
Claim 1 of Japanese Patent Application Publication No. H7-82,889 (1995) has disclosed a waterproof connector characterized comprising a shell, a rubber insulator detachably inserted in said shell, a plurality of relay contacts provided on said rubber insulator, press-fitting contacts each adapted to removably contact said relay contact, a ground lug mounted on either of said relay contact and said press-fitting contact to electrically contact said shell, a front insulator detachably inserted in said shell and holding the fitting of said relay contact and said press-fitting contact, a rear insulator detachably inserted in said shell and engaging said press-fitting contact to cause said press-fitting contact to be anchored to said front insulator, a retainer ring detachably anchored in said shell and causing said rear insulator to be anchored in said shell, and an O-ring detachably provided in said shell and adapted to abut against a mating connector.
In FIGS. 2 and 3 and the paragraph [0014] of the official gazette (Japanese Patent Application Publication No. H7-82,889), concerning the grounding structure using a ground lug, there is described “The ground lug 9 is formed from square wires having a diameter of about 0.5 mm, and upon mounting the ground lug 9 on a relay pin 4′, the ground lug 9 is secured at a part 9b to the relay pin 4′ by pressure welding. When a rubber insulator 5 provided with the relay pin 4′ is inserted into the shell 1 by press-fitting, a part 9a of the ground lug 9 is inserted into the shell 1 by press-fitting so that a chromate film on a zinc plating layer of the shell 1 is broken by the part 9a of the ground lug 9, thereby obtaining continuity between the ground lug 9 and the shell 1. Moreover, the contact resistance between the relay pin 4′ and the shell 1 is less than 0.1Ω.”
In order to comply with the safety standard, recently, the need to employ a reliable ground connection with a shell has been increased. For this purpose in many cases, as disclosed in the Patent Literature 1, one (core) of a required number of contacts is connected to a ground lug, and further the ground lug is brought into contact with a shell so as to obtain continuity between the one of the contacts and the shell, thereby achieving a grounding structure. However, one of the required number of contacts has to be used for the grounding so that a further contact must be complicatedly added to the required contacts.
Even if the use of one contact among the required ones for grounding is accepted, there has been an increasing customer's demand for a structure enabling contacts to be easily inserted into and removed from a housing and further enabling the housing to be simply inserted into and removed from a shell.
Depending upon customers or consumers, moreover, there have been demands for a grounding procedure being capable of suitably choosing by a user whether one contact among a required number of contacts or a separate ground terminal is used for grounding.